• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.4
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• pp.274-280
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• 2003

If a sinusoidal excitation force moves back and forth along a structure with a certain frequency, the structure will be excited with the difference frequency of these two frequencies. A low frequency vibration shaker has been developed using this force frequency shifting without actually moving a shaker The shaker consists of an ordinary eccentric mass shaker, a plate, constant springs, and time varying dampers. The dampers are turned on and off in a sequential manner to simulate a traveling slide of an excitation force. The operation of the shaker is simulated by solving the equations of motion of the shaker. Characteristics of the shaker have been found and they can be utilized to design efficient low frequency shakers.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1042-1048
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• 2007

This work analytically investigated the radiated noise of a helical gear-housing system due to the excitation of helical gears. The helical gears were modeled as a 12-degree of freedom mass-spring-damper system; the shaft was modeled as a rod, a beam, and a torsional shaft; and the gear housing was modeled as a clamped circular plate with viscous damping. The modeling of this system used transfer matrices for helical gears, shafts, and bearings. Damping for both the bearings and the plate were obtained by modal testing. For the evaluation of noise, sound pressure from the plate due to the force and the moment in both radial and tangential directions was analytically derived by the Rayleigh integral. The analytical derivation and parameters from the experiment were applied to an analysis of noise for the two sets of helical gears with differing gear ratios. The analysis showed that the moment excitation in both helical gears contributed more to the noise of the plate than axial force excitation.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.185-192
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• 2002

This paper focused on the dynamic behavior of camshaft in a direct acting type valve train system. To investigate camshaft behavior, transient vibration analysis is performed by using the transfer matrix method. The camshaft is treated as lumped mass system supported by spring and damper. Front the presented analytical model, we could predict dynamic behavior of camshaft, shaft locus within bearing and bearing load. The presented mode and results will be very helpful to design the optimal camshaft and valve train system.

• Journal of Institute of Convergence Technology
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• v.5 no.2
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• pp.37-42
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• 2015

This paper presents the effects of the computational time-varying delay on the stability of the haptic system that includes a virtual wall and a first-order-hold method. The model of a haptic system includes a haptic device model with a mass and a damper, a virtual wall model, a first-order-hold model and a computational time-varying delay model. In this paper, the maximum of the computational time-varying delay is assumed to be as much as the sampling time. Using the simulation, it is analyzed how the sample-hold methods and the computational time-varying delay affect the maximum available stiffness. As the maximum of computational time-varying delay increases, the maximal available stiffness of a virtual wall model is reduced.

• International Journal of Precision Engineering and Manufacturing
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• v.3 no.4
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• pp.94-100
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• 2002

The conventional sliding mode control (SMC) technique requires a priori knowledge of the upperbounds of disturbances and/or modeling uncertainties to assure robustness. This, however, may not be easy to obtain in practical situation. This paper presents a new methodology, a sliding mode control with disturbance estimator (SMCDE), which offers a robust control performance without a priori knowledge about the disturbance. The proposed technique is featured by an average value of the imposed disturbance over a certain period. A nonlinear spring-mass-damper system and a two-link robot system are adopted as illustrative application examples. Control performances such as estimation error and tracking error are compared between the proposed methodology and conventional scheme.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.172-175
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• 2002

Sloshing of fuel in a liquid propellant tank is an important part of the dynamic and the stability analysis of the rocket. Baffles are installed in a propellant tank to reduce the instability due to sloshing. Multi degree of spring-mass-damper model was used to model sloshing of fuel in an axisymmetric tank. The natural frequencies and damping ratios are estimated. In order to verify the estimated natural frequencies and damping ratios, tests are performed for the real propellant tank of KSR-III with single ring baffle. Results of fuel sloshing analysis are compared with those of tests.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.182-186
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• 2002

If a sinusoidal excitation force moves back and forth along a structure with a certain frequency, the structure will be excited with the difference frequency of these two frequencies. A low frequency vibration shaker has been developed using this force frequency shifting without actually moving a shaker. The shaker consists of an ordinary eccentric mass shaker, a plate, constant springs, and time varying dampers. The dampers are turned on and off in a sequential manner to simulate a traveling slide of an excitation force. The operation of the shaker is simulated by solving the equations of motion of the shaker. Characteristics of the shaker have been found and they will be utilized to design efficient low frequency shakers.

• Journal of KSNVE
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• v.9 no.4
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• pp.754-760
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• 1999

The valve motions of a reciprocating compressor generate the pressure fluctuation at the plenum which is a main source of noise and vibration of a compressor unit. But a cycle of a compressor process consists of complicated phenomena interacting in a short period of time. A mathematical model is developed by simplifying and idealizing the complicated phenomena to simulate the compressor process. The governing equations about the pressure and working fluid flow are developed from the unsteady Bernoulli equation. The pressure fluctuations at the plenums are derived from the Helmholz's resonator model. The valves are modeled as one degree of freedom spring-mass-damper system. This model is verified by the experimental results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.6 s.99
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• pp.712-717
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• 2005

This paper presents a system identification method for multi-input, multi-output (MIMO) systems, by which a rational polynomial transfer function model is identified from experimentally determined frequency response function data. Analytically determined information is incorporated in this method to obtain a more reliable model, even in the frequency range where the excitation energy is limited. To verify the suggested method, shaking table test for an actively controlled two-story, bench-scale building employing an active mass damper is conducted. The results show that the proposed method is quite effective and robust for system identification of MIMO systems.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.210-214
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• 2007

A simulation program has been developed to evaluate operator seat vibration for earth-moving machinery and decide whether a seat meets the requirements imposed by ISO 7096. An operator seat is assumed as a linear system composed of a mass, a spring, and a damper mounted on a platform. The program evaluates the transmissibility at resonance, and the SEAT factors for a light person and a heavy person. The developed program can be utilized effectively in designing a new operator seat.